A commonly used phenol production method is decomposition of cumene hydroperoxide to phenol, acetone, and α-methylstyrene in the presence of an acidic catalyst. Another method to produce phenol is oxidizing at least a portion of a feed comprising cyclohexylbenzene to produce an oxidation composition comprising cyclohexyl-1-phenyl-1-hydroperoxide. The oxidation composition may then be cleaved in the presence of an acidic catalyst to produce a cleavage reaction mixture comprising the acidic catalyst, phenol and cyclohexanone.
Typically, the acidic catalyst used in the phenol production processes is a strong, and comparably low corrosive inorganic acid, such as sulfuric or phosphoric acid. The acidic catalyst must be removed or neutralized to prevent further, undesired reactions in the downstream purification steps that produce phenol and other products. Commercial processes for the manufacture of phenol use inorganic bases, ion exchange resins, organic amines or a combination thereof to remove acidity from crude product stream.
The use of a strong base, such as sodium hydroxide or potassium hydroxide to neutralize the acidic catalyst is not desirable because it is difficult to achieve accurate pH control in a neutralization reaction between a strong acid and a strong base. Moreover, metal hydroxides generate salts that have a propensity to deposit on heat exchange surfaces, causing fouling and decreasing efficiency. Since ion exchange resins are temperature sensitive, the crude product stream must be cooled substantially prior to contact with the resin. The need to cool the product stream increases energy costs significantly because the crude product stream must then be re-heated prior to downstream purification operations. A further drawback of ion exchange resins is that they must be regenerated frequently, a labor-intensive and costly process which also results in formation of large amounts of aqueous waste. Moreover, ion exchange resins give a highly variable final pH in the crude produce stream, adversely affecting final product yields, and can also release alkali salts which cause fouling of equipment. Organic amines like methylpentamethyenediamine (MPMD) and hexamethylene (HMDA) are commonly used as neutralizers, but their neutralization efficiency is not good enough.
The problem addressed by this invention is the provision of an improved method for the production of phenol, that avoids or mitigates the foregoing neutralization problems.